Conventionally, as a Parkinson's disease treatment, L-Dopa therapy has been known, in which L-Dopa known as a therapeutic preparation for the disease is administered to supplement dopamine. Nevertheless, the L-Dopa therapy has problems: for example, long-term continuous administration is required, but the long-term continuous administration gradually reduces the drug effect, and a diurnal variation in the symptoms is produced very frequently. Hence, ropinirole was developed as a drug to solve such problems with the L-Dopa therapy. Recently, for the purpose of disease treatments for Parkinson's disease, restless legs syndrome, and the like, various studies have been conducted on preparations which contain ropinirole and/or pharmaceutically acceptable salts thereof.
For example, International Application Japanese-Phase Publication Nos. 2009-518376 (PTL 1) and 2007-516265 (PTL 2) each disclose a composition for topical administration, containing ropinirole, as an external preparation such that side effects in the stomach and intestines can be avoided. Furthermore, efforts have been made also to study transdermal preparations because it is easy to remove a transdermal preparation when a side effect occurs and it is easier to adjust the amount of the drug to be administered. For example, International Application Japanese-Phase Publication Nos. 2001-518058 (PTL 3) and Hei 11-506462 (PTL 4) each disclose, as a transdermal preparation containing ropinirole, a patch including a support layer and an adhesive agent layer containing ropinirole. However, the patches described in PTLs 3 and 4 above have problems that the skin permeability of ropinirole still has not been sufficient, making it difficult to keep the ropinirole concentration in the plasma at a sufficiently high level.
Meanwhile, the drug is normally distributed in the market in the form of an acid addition salt because of the handleability and the stability. When the drug in the form of acid addition salt is directly used in a transdermal preparation or the like, the skin permeability of the drug tends to be reduced. It is known that the drug is preferably used in a free form from the viewpoint of skin permeability. For example, International Publication No. WO2009/107478 (PTL 5) discloses a patch including an adhesive agent layer containing: ropinirole in a free form (free ropinirole) and a metal salt produced by a reaction of a ropinirole acid addition salt and a metal-ion containing desalting agent in an equivalent mole or less to the acid addition salt; and an adhesive base free of a hydroxyl group and a carboxyl group.